In a system involving a body of liquid to which a treating agent is added, maintaining the proper feed level for the agent is essential for optimal performance. An improper feed rate of treating agent can lead to serious problems. For example, severe corrosion and deposit formation can rapidly occur on heat-exchanger surfaces in cooling water systems when incorrect levels of treating agent are used. One common method of estimating the concentration of a treating agent focuses on measuring the level of an active component in the treatment formulation (e.g., polymeric scale inhibitor, phosphate, or organophosphate). That technique is often unsatisfactory due to one or more of the following problems:
background interferences from the system liquid or materials contained in the liquid; PA0 analytical methods require bulky and costly equipment; PA0 time-consuming, labor-intensive analyses are not compatible with continuous monitoring; and PA0 inaccurate readings result from degradation or deposition of active component within the system.
An alternative method of determining treatment feed rates is to add tracer compounds to the formulation or system. This method helps circumvent the degradation, deposition, and background interference problems that commonly occur when measuring the level of an active component in a treatment formulation. However, quantitation of low tracer levels commonly magnifies problems associated with expensive equipment and time-consuming test methods. Additional factors which must be considered are cost and environmental acceptability of the tracer. For example, radioactive tracers are detectable at very low levels, but are generally expensive and unacceptable due to environmental and health concerns.
Ultimately, compounds selected as tags or tracers serve as indices to other chemicals present in an aqueous system. These tags or tracers are selected to fulfill certain criteria. For example, certain tracers are detectable by electronic devices on a continuous or semi-continuous basis. In addition, certain tracers provide measurements of concentration that are accurate, repeatable and/or capable of being performed on many different waters (i.e., clean, turbid, hard, soft, etc.) and variations of these waters. To achieve these goals, the tracer selected is preferably not present in significant quantities within the waters tested. In addition, the tracers selected must be quantifiable by tests that are not interfered with or biased by other chemical compounds normally present in the water to be tested. The tracers selected are preferably inert and stable in the treatment water and do not reduce the activity of the treatment chemicals themselves.
The tracers must be soluble in the waters to be tested and must be compatible with the treatment chemicals with respect to formation, storage, freeze-thaw recovery, etc. Most importantly, the tracers must show a minimal incorporation into the equipment scale as compared to the treatment chemicals. Incorporation is the transfer of tracer from the treated aqueous system to the surfaces of the system equipment. Last, the tracers should not present any sort of environmental problems in the event of discharge. To avoid costly disposal methods, it is preferable for the tracer to be functional at levels sufficiently low so that discharge does not pose a health concern. The tracer is preferably non-toxic at high concentrations. The tracer must be sufficiently safe so that its use at the concentrations desired conforms to all governmental regulations.
Chromium VI (e.g. bichromate, Cr.sub.2 O.sub.7.sup.-2) has been used as a tracer in cooling waters in industrial cooling water systems. However, the Environmental Protection Agency and Occupational Safety Hazard Administration have restricted the use of Chromium VI in industry. Also chromium (VI) is a reactive, oxidizing agent and alternative tracer compounds are needed.
The present invention is based on the discovery of a new class of tracer compounds that meet the above specified criteria.